Process for forming a deposited film using a light transmissive perforated diffusion plate

ABSTRACT

A process for forming a deposited film on a substrate including generating a plasma in a plasma generating chamber via a light transmissive perforated diffusion plate which is located adjacent to a reaction chamber containing the substrate. The plasma thereby excites a gas, which is introduced into the reaction chamber through the light-transmissive perforated diffusion plate. A gaseous starting material for forming the deposited film is introduced into the reaction chamber and reacts with the excited gas. A deposited film is formed on the substrate while irradiating the substrate with a light scattered by the light-transmissive perforated diffusion plate.

This application is a division of application Ser. No. 07/987,786 filedDec. 9, 1992, now U.S. Pat. No. 5,433,787.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a process for forminga deposited film. In particular, the present invention relates to anapparatus and a process for forming a deposited film which are capableof forming SiO₂ or SiN film with high quality and uniformity on asubstrate.

2. Related Background Art

Deposited film formation apparatuses play an important role inmanufacture of semiconductor devices and electronic circuits,particularly of ultra LSIs. For example, plasma CVD apparatuses areemployed to form SiN films for use as a final protective film; plasmaCVD apparatuses or atmospheric pressure CVD apparatuses are employed toform SiO₂ film for interlayer insulation; and sputtering apparatuses areemployed to form thin aluminum films for wirings.

Regarding SiO₂ films for interlayer insulation, as the devices are beingmade finer, three-layer structure has come to be used in whichspin-on-glass (SOG), which is excellent in step-covering property, isinterposed between SiO₂ films for insulation which are formed by plasmaCVD or atmospheric pressure CVD. However, this type of interlayerinsulation film is liable to cause cracks therein owing to shrinkageafter post-heat-treatment of SOG. Therefore the film has to be formed inseveral steps in order to suppress the occurrence of cracks. As aresult, there is a problem of increasing step number. For one-stepformation of an SiO₂ film having excellent step-covering property, amethod of atmospheric pressure CVD is being investigated in which O₃ andtetraethyl orthosilicate (Si(OC₂ H₅)₄, abbreviated to TEO, also calledtetraethoxysilane) are used as starting gaseous materials. In theatmospheric pressure CVD, however, the reaction proceeds mainly bysurface reaction, so that the reaction is incomplete as a whole. Thismethod may sometimes cause cracks in the film or corrosion of aluminumwiring on the film by contamination with a large amount of radicals ofhydroxyl, ethyl, etc., especially at a low temperature below 400° C.required to form interlayer insulation films. In contrast, the plasmaCVD enables formation of SiO₂ films with better quality than theatmospheric pressure CVD at temperature below 400° C.

In the atmospheric pressure CVD and plasma CVD, Irradiation of lightduring film formation is known to accelerate the film formationreaction. Since, in principal, the deposited film-forming apparatuseswhich utilize light enable treatment at a lower temperature with lessdamage, they are expected to be used and they are now starting to beapplied to cleaning and annealing processes.

In the formation of a deposited film by the method utilizing light, awindow for introducing the light is provided generally in a reactionvessel. However, the film is formed also on the face of the window,thereby blurring the window and reducing greatly the illuminance of theincident light introduced into the reaction vessel. A method forpreventing the blurring of the window such as a grease-coating method, agas-purging method and the like are reported. FIG. 9 and FIG. 10 areschematical views of structures of the conventional depositedfilm-forming apparatuses employing respectively a grease-coating methodand a gas-purging method to prevent the blurring of the lightintroduction window.

In the deposited film-forming apparatus as shown in FIG. 9, atransparent light introducing window 61 constitutes the upper face of acylindrical reaction vessel 50, and an illumination system 60 as thelight source is provided in contact with the upper face of the lightintroducing window 61. An evacuation opening 59 connected to anevacuation pump not shown in the drawing is provided at the bottom ofthe reaction vessel 50. Above the evacuation opening 59 of the reactionvessel 50, a supporting member 53 is provided for supporting a substrate52 to be treated. The starting gases for the reaction are fed into thereaction vessel 50 through a ring-shaped starting gas-introducing tube58. In this apparatus, the starting gas-introducing tube 58 is placed bythe side of the substrate 52 to feed the starting gases from theperiphery of the substrate 52, so that the light from the illuminationsystem 60 is not intercepted and is illuminated uniformly onto thesubstrate 52. Onto the inside face of the light introducing window 61 ofthe reaction chamber, a transparent grease is applied. With thisconstitution of the deposited film-forming apparatus, film formation andblurring on the light introducing window is prevented since theinorganic thin films conventionally used for semiconductor devices areless liable to adhere onto grease.

The deposited film-forming apparatus as shown in FIG. 10 differs fromthe one in FIG. 9 in that a perforated separation plate 62 is providedto separate the reaction chamber into an upper space and a lower spaceof the chamber vessel 50: the upper space being a purge chamber 54 andthe lower space being a reaction chamber 51. The substrate 52, thesupporting member 53, the starting gas-introducing tube 58, anevacuation opening 59 are placed in the reaction chamber 51. Purge gasintroducing tubes 57 are placed in the purge chamber 54. The purge gasdoes not participate directly in the reaction, but serves to keep thepressure in the purge chamber 54 higher than that of the reactionchamber 51. In the deposited film-forming apparatus shown in FIG. 10,the light-introducing window 61 is not coated with grease. In thisdeposited film-forming apparatus, diffusion of the starting gases intothe gas purge chamber 54 is prevented by maintaining the pressure in thepurge chamber 54 higher than that in the reaction chamber 51, therebythe film is formed on the substrate 52 without formation of a film onthe light introducing window 61.

In the deposited film-forming apparatuses employing light irradiation asdescribed above, the starting gas is introduced from the periphery ofthe substrate so that light is irradiated on the substrate uniformly.Therefore the apparatuses have a disadvantage that the pressure andcomposition of the starting gas are not uniform on the surface of thesubstrate and the film thickness may vary depending on the pressure offilm formation. Further, in the case where grease is applied to preventthe film formation on the light introducing window, the apparatuses havethe disadvantage that a grease component evaporated by light irradiationis liable to contaminate the formed film, and if the illuminance of thelight is increased to promote the film formation, the grease itself maycause the blurring of the window. In the gas purge method, when thepressure is insufficient to purge the starting gases, a film may depositon the separation plate to cause blurring and thereby form a non-uniformdeposited film even if the separation plate is transparent.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and aprocess for forming a deposited film which solve the problems of theprior art as described above.

Another object of the present invention is to provide an apparatus and aprocess for forming a deposited film uniformly on a substrate with lessblurring of a light introducing window.

A further object of the present invention is to provide an apparatus anda process for forming a deposited film which are capable of forming athin film having good step-covering property with high quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, FIG. 2 and FIG. 3 are schematical views showing examples of adeposited film-forming apparatus of the present invention, respectively.

FIG. 4 is a schematical view showing one example of a perforateddiffusion plate employed in the deposited film-forming apparatus of thepresent invention.

FIG. 5 is a cross-sectional view of the deposited film-forming apparatusas shown in FIG. 4 taken along a line A-A'.

FIG. 6 and FIG. 7 are schematical views showing examples of a depositedfilm-forming apparatus of the present invention, respectively.

FIG. 8 is a graph showing the dependency of a deposited film formationrate on the pressure in the reaction chamber.

FIG. 9 and FIG. 10 are schematical views showing example of depositedfilm-forming apparatus of prior art, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the deposited film-forming apparatus of thepresent invention are described below.

A first embodiment of the deposited film-forming apparatus of thepresent invention comprises a reaction chamber, a supporting memberprovided in the reaction chamber for holding a substrate, a plasmagenerating chamber adjacent to the reaction chamber with interpositionof a light-transmissive perforated diffusion plate wherein at least apart of the plasma generating chamber is made of a light-transmissivemember, a plasma-generation means for generating plasma in the plasmagenerating chamber, a first gas-introduction means for introducing a gasinto the reaction chamber, a second gas-introduction means forintroducing another gas into the plasma generating chamber, anevacuation means for evacuating the reaction chamber and the plasmagenerating chamber, and a light source provided outside the plasmagenerating chamber for irradiating light to the substrate held on thesupporting member through the plasma generating chamber and theperforated diffusion plate, wherein the perforated diffusion plate has alight-scattering diffusion face at least at the side of the reactionchamber.

A second embodiment of the deposited film-forming apparatus of thepresent invention comprises a reaction chamber, a supporting memberprovided in the reaction chamber for holding a substrate, alight-transmissive perforated diffusion plate having at least onelight-scattering face, a purge chamber adjacent to the reaction chamberwith interposition of the light-transmissive perforated diffusion platewherein at least a part of the purge chamber is made of alight-transmissive member, a first gas-introduction means providedinside the perforated diffusion plate for introducing a depositable gasinto the reaction chamber, a second gas-introduction means forintroducing non-depositable gas into the purge chamber, an evacuationmeans for evacuating the reaction chamber and the purge chamber, and alight source provided outside the purge chamber for irradiating light tothe substrate held on the supporting member through the purge chamber.

A third embodiment of the deposited film-forming apparatus of thepresent invention comprises a reaction chamber, a supporting memberprovided in the reaction chamber for holding a substrate, alight-transmissive perforated diffusion plate having at least onelight-scattering face, a plasma generating chamber adjacent to thereaction chamber with interposition of the light-transmissive perforateddiffusion plate wherein at least a part of the plasma generating chamberis made of a light-transmissive member, a plasma generation means forgenerating plasma in the plasma generating chamber, a gas introductionmeans provided inside the perforated diffusion plate for introducing agas into the reaction chamber or the plasma generating chamber, anevacuation means for evacuating the reaction chamber and the plasmagenerating chamber, and a light source provided outside the plasmagenerating chamber for irradiating light to the substrate held on thesupporting member through the plasma generating chamber and theperforated diffusion plate.

A fourth embodiment of the deposited film-forming apparatus of thepresent invention comprises a reaction chamber, a supporting memberprovided in the reaction chamber for holding a substrate, alight-transmissive perforated diffusion plate, a plasma generatingchamber adjacent to the reaction chamber with interposition of theperforated diffusion plate wherein at least a part of the plasmagenerating chamber is made of a light-transmissive member, a plasmagenerating means for generating plasma in the plasma generating chamber,a first gas-introduction means for introducing a depositable gas to thecentral portion of the substrate in the reaction chamber, a second-gasintroduction means provided separated from the first gas Introductionmeans for introducing the depositable gas to periphery of the substratein the reaction chamber, a third-gas introduction means for introducinga non-depositable gas into the plasma generating chamber, an evacuationmeans for evacuating the reaction chamber and the plasma generatingchamber, and a light source provided outside the plasma generatingchamber for irradiating light to the substrate held on the supportingmember through the plasma generating chamber and the perforateddiffusion plate.

The preferred embodiment of the process for forming a deposited film ofthe present invention is a method comprising the steps of generating aplasma in a plasma generating chamber adjacent to a reaction chamberprovided with a substrate for forming a deposited film withinterposition of the light-transmissive perforated diffusion plate;introducing a gas excited by the plasma through the perforated diffusionplate into the reaction chamber; introducing a gaseous startingsubstance reactive to the excited gas into the reaction chamber to causereaction; and forming a deposited film on the substrate placed in thereaction chamber under irradiation to the substrate with light scatteredby the perforated diffusion plate.

In the first embodiment of the present invention, a perforated diffusionplate is employed which has a light-scattering diffusion face at leaston the side of a reaction chamber. Therefore, illuminance on a substrateis made more uniform by diffusion of incident light by the perforateddiffusion plate. The perforated diffusion plate gives a difference ofthe internal pressure between the plasma generating chamber and thereaction chamber, which prevents nearly completely the diffusion of thedepositable gas (the starting gas) from the reaction chamber into theplasma generating chamber, thus preventing the film adhesion on thelight introduction window. Even if a film adheres on the perforateddiffusion plate and the irregularity of the film cause additional lightscattering, the illuminance does not vary significantly on the substratesurface since the incident light has been already scattered by thediffusion face.

The diameter of the through-holes of the perforated diffusion plateshould not exceed about 3 mm, since a larger diameter of thethrough-holes makes the illuminance on the substrate less uniform byforming the shadow of the through-holes on the substrate. The openingarea ratio of the through-holes is preferably in the range of from 1% to5% based on the whole area of the perforated diffusion plate. If theopening area ratio is more than 5%, the pressure difference between theplasma generating chamber and the reaction chamber becomes insufficient,whereby gas diffusion from the reaction chamber becomes significant,making the prevention of attaching the film to the light introductionwindow less effective, etc. On the other hand, if the opening area ratiois less than 1%, the pressure in the plasma generating chamber risesexcessively to retard the plasma generation. The plasma is generated inthe plasma generating chamber by a known method, for example, byapplication of high frequency power or microwave power to the plasmagenerating chamber. In such a method, the plasma generating chamberpreferably is in a cylindrical form and has a side wall constructed of aquartz tube for supplying the energy effectively into the plasmagenerating chamber.

In the second and the third embodiments of the present invention, theapparatus comprises a first gas-introduction means inside a perforateddiffusion plate for introducing a depositable gas into the reactionchamber and a second gas-introduction means for introducing anon-depositable gas into a purge chamber or a plasma generating chamber.Thereby both the depositable gas and the non-depositable gas are allowedto flow uniformly from the perforated diffusion plate to the substrate,which enables uniform film formation on the substrate. Such a type ofperforated diffusion plate, for example, has a constitution as follows.Two transparent plates are placed at an interval. The plate at the sideof the reaction chamber has a large number of holes so as to flow thegas between two plates and supply to the reaction chamber, and tubes areprovided which penetrate through the plates at the side of the purgechamber and at the side of the reaction chamber so the two chamberscommunicate as shown in FIGS. 4 and 5.

The inside diameter of the tubes penetrating the two plates and thediameter of the holes provided on the plate at the side of the reactionchamber are both preferably not larger than 3 mm. The sectional areabetween the two plates constituting the perforated diffusion plate ispreferably sufficiently large in comparison with the area of holesprovided on the plate at the side of the reaction chamber in order tofeed the depositable gas uniformly.

In the fourth embodiment of the present invention, the apparatus isprovided with a first gas-introduction means for feeding a depositablegas above the central portion of the substrate in the reaction chamber,and a second gas-introduction means separated from the firstgas-Introduction means for feeding the depositable gas above theperiphery of the substrate in the reaction chamber. Thereby, the amountof the depositable gases fed to the periphery portion of the substrateand the central portion are controllable independently. This enablesuniform film formation by supplementing the film thickness at thecentral portion in comparison with the conventional apparatus where thecentral portion of the film tends to be thin. In this apparatus, thefirst gas introduction tube is desirably a light-transmissive fine tubehaving through-holes on the side wall thereof so as not to form shadowson the substrate, and is desirably has a rectangular cross-section so asnot to condense the light.

In the first to the fourth embodiments, the depositable gases to be feddirectly to the reaction chamber includes organic silane compounds suchas SiH₄, Si₂ H₆, SiCl₂ H₂, alkoxysllane, siloxane, and silanol; organiccompounds such as diborane, arsine, phosphine. alkane, alkene, alkyne,alcohol, and benzene; organoaluminum compounds, organotitaniumcompounds, WF₆, organotungsten compounds, organomolybdenum compounds,organotantalum compounds, and so forth. The non-depositable gases to befed to the purge chamber or a plasma generating chamber includes O₂, O₃,N₂ O, H₂ O, N₂, NH₃, N₂ H₄, H₂, Ar, and so forth.

With the apparatus of the present invention, SiO₂ film can be formed byreacting an oxidizing gas excited by plasma with a silanol having atleast one hydroxyl group bonded to the silicon atom. In this process,interaction with the substrate surface is decreased and the surfacediffusion is promoted, thus the resulting SiO₂ film is improved in thestep-covering property. Further, the presence of silanol mainly having ahydroxyl group serves to decrease the contamination with carbon into thefilm. The irradiation to the substrate with ultraviolet or visible lightdecreases contamination with hydroxyl, and improves further the qualityof the film.

The aforementioned oxidizing gas includes O₂, O₃, N₂ O, etc. The silanolmay be either an organic silanol containing an alkyl group, etc. or aninorganic silanol containing no alkyl group, etc. but the silanol ispreferred which has a higher saturated vapor pressure and has lesscarbon atoms. The silanol may be formed, just before the reaction of thefilm deposited on the substrate, by reaction of an organic or inorganicsilane with water to increase the feed rate. The plasma for exciting theoxidizing gas may be generated either by high frequency of from about 1to about 300 MHz or by microwave of from about 0.9 to about 5 GHz. Toincrease the electron density, a magnetic field may be applied duringplasma generation.

The present invention is explained in more detail with reference to thefollowing examples. However, the present invention should not be limitedby these examples.

EXAMPLE 1

FIG. 1 illustrates schematically an example of a deposited film-formingapparatus of the present invention. This deposited film-formingapparatus corresponds to the above described first embodiment of thepresent invention, and comprises a perforated diffusion plate having alight-scattering diffusion face at least at the reaction chamber side ofthe perforated diffusion plate.

In the deposited film-forming apparatus, the cylindrical reactionchamber 1 has at the bottom thereof an evacuation opening 9 connectedthrough a conductance valve not shown in the drawing to an evacuationpump not shown in the drawing. A supporting member 3 is provided Justabove the evacuation opening 9. A substrate 2 to be treated forformation of a film is supported by the supporting member 3. A startinggas introduction tube 8 in a ring shape is provided above the substrate2 in the reaction chamber 1 so as to introduce a depositable gastherein. The starting gas introduction tube 8 is connected to a startinggas source not shown in the drawing. A perforated diffusion plate 12partitions the reaction chamber 1 and a plasma-generating chamber 4. Theperforated diffusion plate 12 is made of a light-transmissive materialsuch as fused quartz and has many through-holes of not more than 3 mm indiameter at an opening area ratio of from 1 to 5%. The reaction chamber1 and the plasma-generating chamber 4 are communicated through theperforated diffusion plate 12. The face of the perforated diffusionplate 12 is ground like frosted glass at the side of the reactionchamber 1 to be light-diffusive.

The side wall of the plasma generating chamber 4 is made of a quartztube 5. Electrodes 6 for generating high-frequency or microwave plasmadischarge are attached to the outside of the quartz tube 5. Theseelectrodes 6 are connected to a high-frequency source or a microwavesource. Inside the plasma generating chamber 4, a non-depositable gasintroduction pipe 7 is provided along the inside wall of the chamber tointroduce a non-depositable gas into the plasma generating chamber 4.This non-depositable gas introduction pipe 7 is connected to anon-depositable gas source not shown in the drawing. The upper face ofthe plasma generating chamber 4 serves as a transparentlight-introduction window 11. An illumination system 10 is provided as alight source near and above the light-introduction window 11.

The procedures for forming a deposited film by use of the deposited filmforming-apparatus are described below.

A substrate 2 is held on a supporting member 3, and the reaction chamber1 and the plasma generating chamber 4 are evacuated. Since manythrough-holes are provided in the perforated diffusion plate 12, notonly the reaction chamber 1 but also the plasma-generating chamber isevacuated by evacuation from the evacuation opening at the reactionchamber 1. When a predetermined vacuum degree is achieved, theillumination system 10 is operated. The light from the illuminationsystem 10 is introduced through the light-introduction window 11 and theperforated diffusion plate 12 onto the surface of the substrate 2.Simultaneously, a gas for plasma generation is introduced through thenon-depositable gas-introduction tube 7 into the plasma generatingchamber 4, and a depositable gas as the starting gas is introducedthrough the starting gas introduction tube 8. Then high frequency poweris applied to the electrodes 6. The pressure is naturally higher in theplasma-generating chamber 4 than in the reaction chamber 1, sinceevacuation is practiced at the reaction chamber 1.

As the result, plasma discharge occurs in the plasma-generating chamber4, the non-depositable gas is excited by plasma, and the excited gasmoves through the perforated diffusion plate 12 into the reactionchamber. In the reaction chamber 1, the excited gas reacts with thedepositable gas to form a film on the substrate 2. The perforateddiffusion plate 12, which has a light-diffusive surface at the side ofthe reaction chamber 1, diffuses the light from the illumination system10 to give uniform illuminance on the substrate 2, resulting in uniformfilm formation. The higher pressure in the plasma-generating chamber 4than in the reaction chamber 1 prevents the diffusion of depositable gasto the plasma-generating chamber 4, thereby preventing adhesion of afilm on the light introduction window 11, etc. Although some filmsadhere on the perforated diffusion plate 12, light scattering caused bythe irregularity of the newly adhered film affects little theilluminance on the substrate 2 because the light has already beenscattered by the diffusion face of the perforated diffusion plate 12.

When the film has been formed in a predetermined thickness, theapplication of high frequency or microwave power, and the introductionof the depositable gas and the non-depositable gas are stopped. Then thesubstrate 2 having the formed film is taken out.

EXAMPLE 2

This Example shows formation of an SiO₂ film on a substrate 2 with useof high frequency for plasma generation described in Example 1. FIG. 2illustrates schematically the deposited film-forming apparatus employedin this Example.

This deposited film-forming apparatus comprises magnets 13 within theelectrodes 6 with the magnetic pole axis directed vertically, inaddition to the apparatus employed In Example 1, in order to apply amagnetic field vertically to the electric field for the plasmageneration. The electrodes 6 are connected to a high frequency source25. As the illumination system 10, an illumination system comprising axenon lamp and an integrator was used. The perforated diffusion plate 12made of a fused quartz plate grounded like frosted glass to a roughnessof 0.2 mm at the side of the reaction chamber 1, and havingthrough-holes of 2 mm in diameter with the opening area ratio of 2% wasused. When a substrate of 150 mm in diameter was used, variation ofilluminance on the substrate 2 was ±2%, which was better than thevariation of ±5% in conventional light-transmissive perforated plateshaving no diffusion face.

A film was formed by supplying O₂ as a non-depositable gas at a rate of2 slm (1 slm=1000 sccm) into the plasma generating chamber 4, supplyingtetraethyl orthosilicate as a depositable gas at a rate of 200 sccm intothe reaction chamber 1, and generating plasma with application of highfrequency power of 1 kW to the electrodes 6. After one hundred times ofrepetition of film formation each for 2 minutes, the light transmittanceof the light introduction window was measured, and found that thetransmittance changed little from the value before the start of the filmformation. The vertical transmittance at the point at a distance of 50mm from the center of the perforated diffusion plate 12 was 61%,therefore the change of the transmittance was little-in comparison withthe value of 64% before the film formation.

On the contrary, in the case where the conventional transparentperforated plate was used in place of the aforementioned perforateddiffusion plate 12, the transmittance changed from 89% (before theformation) to 63% (after the film formation), and the illuminance on thesubstrate changed greatly. Accordingly, it is clear that, with thetransparent perforated plate of this example, absolute illuminance islow, but the uniformity of the illuminance is improved and the change ofthe illuminance during the film formation is little in comparison withthe case where the conventional transparent perforated plate is used.Therefore, the transparent perforated plate of this example ispractically satisfactory.

EXAMPLE 3

This example corresponds to the second embodiment of the presentinvention. FIG. 3 illustrates schematically the constitution of adeposited film-forming apparatus employed in this example. FIG. 4illustrates schematically the perforated diffusion plate employed in theapparatus shown in FIG. 3. FIG. 5 is a sectional view taken along theline 100-100' in FIG. 4.

The deposited film-forming apparatus in this example is similar to theone in Example 1 except that the depositable gas is introduced throughthe inner part of the perforated diffusion plate 15 into the reactionchamber 1 and the plasma discharge is not employed. Therefore, astarting gas introduction tube is not provided in the reaction chamber,but a cylindrical purge chamber 14 is provided in place of the plasmagenerating chamber. The purge chamber 14 has a bottom made of aperforated diffusion plate 15 and has the upper face made of a lightintroduction window 11 as similarly to the plasma generating chamber 4(FIG. 1) of Example 1. A non-depositable gas, such as a purge gas, isintroduced from the non-depositable gas introduction tube 7 into thepurge chamber 14. A heater 20 is provided on the supporting member 3 inthe reaction chamber 1 to heat a substrate 2.

The perforated diffusion plate 15 used in this example comprises twolight-transmissive plates 18 and 19 placed at an interval as shown inFIG. 4 and FIG. 5. The light-transmissive plate 18 at the lowerposition, i.e., at the side of the reaction chamber 1, has a largenumber of ejection holes 17. A depositable gas flows between the twolight-transmissive plates 18 and 19 and is fed to the reaction chamberthrough the ejection holes 17. Tubular through-holes 16 are providedwhich connect the upper light-transmissive plate 19 with the lowerlight-transmissive plate 18. The through-holes 16 are constructed in atubular form such that the non-depositable gas does not enter the spacebetween the two transparent plates 18 and 19. The through-holes 16 andthe ejection holes 17 both have an inside diameter of not larger than 3mm. The space between the light-transmissive plates 18 and 19 isconnected to a depositable gas source not shown in the drawing. Thelower light-transmissive plate 18 is grounded like frosted glass as inExample 1.

By use of this deposited film-forming apparatus, an SiN film was formedas a protective film by use of silicon plate as the substrate 2according to a photo-assisted CVD method. A substrate 2 was placed onthe supporting member 3. The reaction chamber 1 and the purge chamber 14were evacuated to a predetermined vacuum degree. The substrate 2 washeated with a heater 20 to a desired temperature between roomtemperature and several hundred °C. Then NH₃ gas was introduced throughthe non-depositable gas introduction tube 7 into the purge chamber 14,and SiH₄ gas was introduced through the ejection holes 17 of theperforated diffusion plate 15 into the reaction chamber 1. The pressurein the reaction chamber 1 was maintained at a desired pressure of from 1to 20 Torr by controlling a conductance valve (not shown in the drawing)connected to the evacuation opening 9. The light from the illuminationsystem was introduced through the light introduction window 11 and theperforated diffusion plate 15 onto the substrate 12.

As a result, NH₃ gas was allowed to flow through the through-holes 16and SiH₄ gas flowed through the ejection holes uniformly toward thesubstrate 2. The film formation was conducted to obtain a desired filmthickness. Consequently a SiN film was formed uniformly with highquality on the substrate 2.

By changing the kind of the gas to be fed to the reaction chamber 1 andthe purge chamber 14, films of insulating materials such as SiN, SiO₂,Ta₂ O₅, Al₂ O₃, AlN, etc.; semiconductor materials such as amorphous Si,polycrystalline Si, GaAs, etc.; metals such as Al, W, etc. can beformed.

EXAMPLE 4

This example corresponds to the third embodiment of the presentinvention. FIG. 6 illustrates schematically the constitution of adeposited film-forming apparatus employed in this example.

The deposited film-forming apparatus in this example is similar to theone in Example 1 except that the depositable gas is introduced throughthe inner part of the perforated diffusion plate 15 into the reactionchamber 1. Therefore, a gas introduction tube is not provided in thereaction chamber. The perforated diffusion plate 15 is the same as thatemployed in Example 3. Magnets 13 are provided within the electrodes 6with the magnetic pole axis directed vertically In order to apply amagnetic field vertically to the electric field for the plasmageneration. The electrodes 6 are connected to a high frequency source.The supporting member 3 in the reaction chamber 1 is provided with aheater 20 thereon to heat the substrate 2.

By use of this deposited film-forming apparatus, an SiO₂ film was formedfor interlayer insulation on a silicon plate as the substrate 2 by aphoto-assisted plasma CVD method. The substrate 2 was held on thesupporting member 3. The substrate 2 was irradiated with the light fromthe illumination system 10 through the light Introduction window 11 andthe perforated diffusion plate 15. The reaction chamber 1 and the plasmagenerating chamber 4 were evacuated to a predetermined vacuum degree.The substrate 2 was heated by the heater 20 to a desired temperaturebetween room temperature and several hundred °C. Then O₂ gas wasintroduced through the non-depositable gas introduction tube 7 into theplasma generating chamber 4, and tetraethyl orthosilicate was introducedthrough the ejection holes 17 of the perforated diffusion plate 15 intothe reaction chamber 1. The pressure in the reaction chamber 1 wasmaintained at a desired pressure of from 0.1 to 0.5 Torr by controllinga conductance valve (not shown in the drawing) connected to theevacuation opening 9. A high frequency power was supplied to theelectrode 6.

As the result, the magnets 13 in the electrodes 6 localized thegeneration of plasma to the vicinity of the electrodes 6 in the plasmagenerating chamber 4. The O₂ gas was excited by the plasma, and theexcited O₂ gas and the tetraethyl orthosilicate flowed uniformlyrespectively through the through-holes 16 and the ejection holes 17toward the substrate 2. The film formation was conducted to obtain adesired film thickness. Consequently a SiO₂ film was formed uniformlywith high quality on the substrate 2.

By changing the kinds of the gases to be fed to the reaction chamber 1and the plasma generating chamber 4, films of insulating materials suchas SiN, SiO₂, Ta₂ O₅, Al₂ O₃, AlN, etc.; semiconductor materials such asamorphous Si, polycrystalline Si, GaAs, etc.; metals such as Al, W, etc.can be formed.

EXAMPLE 5

This example corresponds to the fourth embodiment of the presentinvention. FIG. 7 illustrates schematically the constitution of adeposited film-forming apparatus employed in this example. FIG. 8 showsthe dependency of the film deposited rates at the central portion andthe peripheral portion of the substrate 2 on the pressure in thereaction chamber 1.

The deposited film-forming apparatus in this example is similar to theone in Example 1 except for the construction of the starting gasintroduction tubes.

A first gas introduction tube 22 made of a transparent small tube isprovided at the position directly above the substrate 2 in the reactionchamber. This first gas introduction tube 22 has a rectangularcross-section, and has a large number of ejection holes on the faceopposite to the substrate 2. A second gas introduction tube 23 in a ringshape is provided above the substrate 2. The first gas introduction tube22 and the second gas introduction tube 23 feed the same starting gasinto the reaction chamber 1, the feeding rates being controllableindependently. A third gas introduction tube 8, which feeds a gasdifferent from the gas fed by the first and the second gas introductiontubes 22 and 23, is provided in the plasma generating chamber 4.

This deposited film-forming apparatus is provided with magnets 13 withinthe electrode 6 with the pole axis directed vertically in order to applya magnetic field vertically to the electric field for the plasmageneration. The electrodes 6 are connected to a high frequency sourcenot shown in the drawing. The supporting member 3 in the reactionchamber 1 has a heater 20 thereon to heat the substrate 2. In theperforated diffusion plate 12, the diameter and the opening area ratioof the through-holes are not limited to those defined in Example 1.

By use of this deposited film-forming apparatus, an SiO₂ film waspractically formed for interlayer insulation on a silicon plate as thesubstrate 2 by a photo-assisted plasma CVD method. The substrate 2 washeld on the supporting member 3. The substrate 2 was irradiated with thelight from the illumination system 10 through the light introductionwindow 11 and the perforated diffusion plate 15. The reaction chamber 1and the plasma generating chamber 4 were evacuated to a predeterminedvacuum degree. The substrate 2 was heated by the heater 20 to a desiredtemperature between room temperature and several hundred ° C. Then O₂gas was introduced through the non-depositable gas introduction tube 8into the plasma generating chamber 4, and tetraethyl orthosilicate wasintroduced through the first gas introduction tube 22 and the second gasintroduction tube 23 into the reaction chamber 1. The pressure in thereaction chamber 1 was maintained at a desired pressure of from 0.1 to0.5 Torr by controlling a conductance valve (not shown in the drawing)connected to the evacuation opening 9. The gas flow rates in the firstgas introduction tube 22 and the second gas introduction tube 23 werecontrolled independently to supply the traethyl orthosilicate gasuniformly on the substrate 2. A high frequency power was supplied to theelectrode 6.

The magnets 13 in the electrodes 6 localized the generation of plasma tothe vicinity of the electrodes 6 in the plasma generating chamber 4. TheO₂ gas was excited by the plasma, and the excited O₂ gas was supplieduniformly through the perforated diffusion plate 12 into the reactionchamber 1. In the reaction chamber 1, the excited O₂ gas reacted withthe tetraethyl orthosilicate under light irradiation from theillumination system 10 to form an SiO₂ film on the substrate 2. The filmformation was conducted to obtain a desired film thickness. Since thelight irradiation and the supply of the tetraethyl orthosilicate gas onthe substrate 2 were uniform, a SiO₂ film was uniformly formed with highquality on the substrate 2.

As a result of examining the relationship between the film forming ratesat the central portion and the peripheral portion of the substrate 2 andthe pressure in the reaction chamber 1, the relationship was shown inFIG. 8. The film forming rates at the central portion was nearly equalto the peripheral portion, although the rates increased with theincrease of the pressure as a whole.

By changing the kind of the gas to be fed to the reaction chamber 1 andthe plasma generating chamber 14, films of materials such as SiN, SiO₂,Ta₂ O₅, Al₂ O₃, AlN, etc.; semiconductor materials such as amorphous Si,polycrystalline Si, GaAs, etc.; metals such as Al, W, etc. can beformed.

EXAMPLE 6

An SiO₂ film for interlayer insulation was formed by a photo-assistedCVD method by use of a deposited film forming apparatus similarly toExample 2. The deposited film forming apparatus which was the same asthat employed in Example 2 (FIG. 2) except that a perforated diffusionplate had light-diffusible at least one face was used.

The procedures of the film formation are as follows. A substrate 2 isheld on the supporting member 3. The reaction chamber 1 and the plasmagenerating chamber 4 are evacuated. The substrate is heated to apredetermined temperature between room temperature and several hundred°C. by a heating means not shown in the drawing. Then the substrate 2 isirradiated with light from the illumination system 10 having a xenonlamp as the light source through the light introduction window 11 andthe perforated diffusion plate 12. An oxidizing gas is supplied throughthe non-depositable gas introduction tube 7 to the plasma generatingchamber 4, and a silanol which has at least one hydroxyl group bondeddirectly to the silicon atom is supplied through the starting gasintroduction tube 8, while the inside pressure of the reaction chamber 1is maintained at a desired level of from 0.05 to 1.0 Torr. Further,plasma is generated in the vicinity of the electrodes 6 in the plasmagenerating chamber 4 by application of a high frequency power of fromabout 100 to 1000 W under application of magnetic field of severalhundred G generated by the magnets 13 to excite the oxidizing gas.Consequently, the excited oxidizing gas moves into the reaction chamber1, and reacts with the silanol to form an SiO₂ film on the substrate 2.When the desired thickness of film has been achieved, the substrate 2having the formed film is taken out.

The practical formation of the film were conducted as below. O₂ gas asthe oxidizing gas was supplied to the plasma generating chamber 4 at arate of 1.5 slm, and silanol Just formed by reaction of silane withwater was supplied to the reaction chamber 1 at a rate of 400 sccm. Theinside pressure of the reaction chamber 1 was 0.1 Torr, the temperatureof the substrate 2 was 300° C., the high frequency power applied to theelectrodes 6 was 400 W, and the magnetic flux density generated by themagnets 13 was 150 G. As the result, a SiO₂ film having excellentcoverage was formed on the substrate with less contamination of hydroxylgroup, etc., particularly carbon.

As described above, the deposited film forming apparatus of the presentinvention has the effects of forming a film uniformly with high qualityon a substrate since the illuminance of the light illuminating thesubstrate and the flow rate and the amount of the gas supplied to thesubstrate are made uniform by use of: (1) a perforated diffusion platewhich is light-transmissive and has a light-scattering diffusion face atleast at the reaction chamber side; (2) a first gas introduction meansfor introducing a depositable gas into a reaction chamber providedinside the perforated diffusion plate, and a second gas introductionmeans for introducing a non-depositable gas into a purge chamber or aplasma generating chamber; or (3) a first gas introduction means forintroducing a depositable gas above the central portion of a substrate,and a second gas introduction means, which provided separately from thefirst gas introduction means, for Introducing the depositable gas abovethe periphery of the substrate in the reaction chamber.

Further the deposited film-forming apparatus of the present invention iscapable advantageously of forming a SiO₂ film, which is of high qualityand improved in step coverage properties, by depositing an SiO₂ film ona substrate by reaction of an oxidizing gas excited by plasma with asilanol having at least one hydroxyl group bonded directly to a siliconatom, thereby decreasing the interaction with the substrate surface andincreasing the surface diffusion.

What is claimed is:
 1. A process for forming a deposited film which comprises the steps of:generating a plasma in a plasma generating chamber provided via a light-transmissive perforated diffusion plate adjacent to a reaction chamber having a substrate arranged therein on which the deposited film is to be formed, thereby exciting a gas; introducing the gas excited in the plasma generating chamber through the light-transmissive perforated diffusion plate into the reaction chamber; introducing a gaseous starting material for forming the deposited film into the reaction chamber so that the excited gas reacts with the gaseous starting material; and forming the deposited film on the substrate arranged in the reaction chamber while irradiating the substrate with a light scattered by the light-transmissive perforated diffusion plate.
 2. The process according to claim 1, wherein the gas to be excited by the plasma is an oxidizing gas and the gaseous starting material is a silanol having at least one hydroxyl group bonded to a silicon atom and the film deposited on the substrate is a SiO₂ film.
 3. The process according to claim 1, wherein the light with which the substrate is irradiated is ultraviolet light or visible light.
 4. The process according to claim 2, wherein the gas is at least one gas selected from the group consisting of O₂, O₃ and N₂ O.
 5. The process for forming a deposited film according to claim 2, wherein the process comprises a step of forming the silanol to be used in the reaction step by reaction of an organic silane with water prior to the reaction step.
 6. The process for forming a deposited film according to claim 2, wherein the process comprises a step of forming the silanol to be used in the reaction step by reaction of an inorganic silane with water prior to the reaction step.
 7. The process according to claim 2, wherein the substrate is irradiated with a ultraviolet light or visible light. 